1. Subject LineThink of your subject line like a movie trailer. If you fail with it there’s very little chance that somebody is going to go pay money to see your movie (or in this case, read the content of your email). So your subject line must clearly state the incentive of opening the email and in most cases should be 50 characters or less. For more information on this MailChimp has a really good article on subject line best practices. http://kb.mailchimp.com/article/best-practices-in-writing-email-subject-lines
While it’s fine (and sometimes more effective) to use HTML based emails with graphics and styled text you must do so VERY CAREFULLY. Unlike browsers, email clients have no real set of standards and each renders slightly differently. Knowing this we must design to the lowest common denominator (for instance Outlook doesn’t support background images within a defined area). In short, you'll need to go back to how we made websites in the late 90s. Everything should use tables and cells (not DIVs) with implicit sizes set, and all styles should be inline. Here’s a tool to preflight your email code and here’s a great article by CampaignMonitor with a lot more detail about best design practices for graphical HTML emails.
3. Content/IncentiveThis is a pretty obvious one, but it’s AMAZING how often it’s overlooked. It’s a classic scenario, somebody from a senior position requests a new email campaign. The designers come up with a great template to house the content… and then nobody puts enough thought into the content itself which was the main point of sending the email in the first place. While I don’t have a blanket statement on how to write good content I do have a couple points to be looked at. First of all explain the benefit or value of what you’re talking about in the first couple sentences. Secondly, don’t get too verbose, when somebody sees a really long email they see this as “extra work” in their day and will most likely close the window and get back to their life. I don’t have a specific word count but put yourself in your audiences shoes and think “would I read through this much content on a busy day at work?”. If the answer is no then you should really consider re-writing a more condensed version. Finally, you should have a prominent and clear call to action for them to go further with your campaign.
4. Lead Capture / Landing Page
This isn’t really part of the email itself, but if the page you’re sending them to is terrible you’re not going to have much luck with your campaign. You can lead a horse to dirty water… but you can’t make it drink. The landing page should clearly relate to the content of the email. It should have a simple, easy to use form (if you are including one) and again shouldn’t be overly verbose. For more information on effective landing page design check out our blog post on it.